guest ::
| Home > Publications database > Korrosionsverhalten von Coat-Mix SiC-Filtermedien unter simulierten Bedingungen der Dieselrußfiltration |
| Home > Publications database > Korrosionsverhalten von Coat-Mix SiC-Filtermedien unter simulierten Bedingungen der Dieselrußfiltration |
| Book/Report | FZJ-2018-06657 |
; ; ;
1994
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/20150
Report No.: Juel-2908
Abstract: The aim of this work was to find out whether a coarse-pored Coat-Mix silicon carbide material is suitable for soot and hot gas filtration. Coat-Mix silicon carbide has a high continuous porosity and good filtration properties. The oxidation behaviour of a coarse-pored and a fine-pored Coat-Mix-SiC in a wet air up to 1000°C und 1350 h has been studied in order to determine the oxidation mechanisms. For comparison a hot-isostatically pressed SiC material (Fa. ESK) has been also studied. The influence of the oxidation on the physical properties (porosity, reactive specific surface and electrical conductivity) and on the mechanical properties (bending strength and permeability) was additionally investigated. In all cases a dense SiO$_{2}$-layer is built and a parabolic rate law is in general obtained. There are no marked differences in oxidation behaviour of the three materials, as can be seen from the activation energy values calculated according to the Arrhenius relation: $\textit{coarse-pored CM-SiC}$ $\approx$ 170 kJ $\cdot$ mol$^{-1}$, $\textit{fine-pored CM-SiC}$ = 152 kJ $\cdot$ mol$^{-1}$ and $\textit{dense SiC}$ 185 kJ $\cdot$ mol$^{-1}$. No corrosive damage of the porous CM-SiC samples is observed. Using gas diffusion and reaction data und pore size it is possible to estimate the depth of the reaction zone at the different oxidation temperatures. Due to the dense silicon oxide layer, which is formed at the geometrical surface and around the internal pores, a decrease in the pore volume and an increase in the density of the samples are determined. The formation of the silicon oxide leads also to a decrease in the reactive specific surface for the fine-pored samples and in contrast to an increase in the reactive specific surface for the coarse-pored samples. The evaluation of long-time tests carried out under the above conditions reveales a clear increace in strength for both CM-SiC grades, amounting to 50 % after oxidation at 1000°C for 840 h. For the dense SiC material only an improvement of the Weibull parameter was calculated. No changes of the open continuous porosity (20 % of the total porosity), which is responsible for the gaspermeability of the filter, are observed and no significant differences in air permeability are found as a function of pressure loss. The formation of the electrically insulating SiO$_{2}$ layers at the internal pores and at the connecting bridges between the SiC grains causes only a slight reduction in the electrical conductivity. This effect depends on the amount of silicon oxide formed and of course on the structure of the specimen, i. e. density and porosity. Soot combustion on the surface of a filter does not appreciably influence the surface structure of the formed silicon oxide during oxidation and thus the air permeability.
|
The record appears in these collections: |
PDF
PDF (PDFA)